This is no big deal, but unowinreg.dll is actually only needed when USE contains both java and odk. However, as the ebuild passes --without-java and --disable-odk directly to openoffice.org ./configure, bypassing ooo-build ./configure, ooo-build will assume it is needed and fail without it. The attached patch will fix this by moving the swiches to ooo-build ./configure and put the download URL within "odk? ( java? ( ... ) )"
Created attachment 99586 [details, diff] the proposed fix
Very good catch, commited this to cvs, thanks for reporting!